1. Field of the Invention
The present invention relates to a vehicle door frame which includes a door sash, a bracket and a belt-line reinforcement member. The bracket and the belt-line reinforcement member are provided in a lower part of the door sash.
2. Description of Related Art
Among vehicle door frames having a belt-line reinforcement member provided in a lower part of a door sash that is shaped along a profile of a door window pane, a type of a vehicle door frame which includes a bracket provided at a corner of the door frame between the door sash and an end of the belt-line reinforcement member is known in the art; such a bracket is fixed to a door panel. This type of vehicle door frame is disclosed in. e.g., Japanese Patent No. 4,463,777.
In the aforementioned type of vehicle door frame, since a joint between the belt-line reinforcement member and the bracket is positioned at a midpoint on a side frame of the vehicle door frame, the vehicle door frame is required to have a sufficient strength especially at this particular joint. More specifically, in the case where the joint is a welded joint, the vehicle door frame is required to have a high buckling strength and have a heat-distortion resistant structure at the joint.